While Part 35 of the English Civil Procedure Rules contains mandatory rules on duty and procedure that expert witnesses and their instructing parties in England and Wales must adhere to, there are currently no equivalent procedural rules under Scottish law, and few Rules of Court that directly affect experts. Nevertheless, the compliance and conduct of an expert witness during a case held in Scotland, can be critical to the outcome of that case and/or to what extent their evidence is relied upon. Instructing parties are therefore advised to keep abreast of common law developments in this area, as well as ensuring that any experts they instruct have received up to date and relevant training on their role and conduct.
There have been several cases over the last few years where the courts have commented on the role and conduct of expert witnesses. Below are a handful of the most relevant cases and their key principles.
Expert’s overriding duty
The position relating to an expert’s duty was historically unclear until the case of Ury Estate Ltd  where the courts confirmed that it is the duty of the expert to help the court on matters within their expertise, and that this duty overrides any obligation to the person who instructed them, or the paying party. As such, expert opinion must be objective, unbiased and uninfluenced by the pressures of litigation; experts must not assume the role of an advocate and their evidence must be confined to their expertise.
Expert's duty to set out the factors on which their opinion is based
T v W  CSOH 44 is a personal injury case where the pursuer, a primary school teacher sought damages from her former employer for psychiatric injuries suffered during her employment. The judgment was granted by Lord Summers.
The pursuer objected to the evidence of the defender’s expert witness Professor Wood claiming that he had not followed, Kennedy v Cordia (Services) LLP  SC (UKSC) in stating ‘’the facts or assumption on which his opinion is based’’ and ‘’the relevant factual evidence so provided’’. The motion was refused by Summers who found that Professor Wood had complied with his duty under Kennedy v Cordia, on the basis that he had acknowledged that he had been supplied with precognitions, and the facts disclosed in his report were based on these precognitions.
Ensuring that experts have the relevant expertise to offer reliable opinion on key issues
Gemmell v Scottish Ministers  SC GLW 16 is a common law negligence case where the pursuer alleged that specific duties were owed to him by the defenders in the exercise of reasonable care. Judgment was granted by Sheriff S Reid.
Whilst Sheriff Reid found the pursuer’s expert witness, Joanne Caffrey to be ‘‘a thoroughly engaging and impressive witness’’, he felt that large sections of her report were entirely irrelevant, and he attached little weight to her evidence as he felt that ‘’she did not have the relevant expertise to offer reliable opinion evidence on the key issues in this case’’.
Rejection of an argument that the expert’s evidence was inadmissible or unreliable
Martin v Hughes  CSOH 109 concerns a claim for unfair prejudice under the Companies Act 2006 by a minority shareholder in a limited company that provides accountancy services. Judgment was given by Lord Clark.
The respondents claimed that the petitioner’s expert, David Bell failed to act as an independent expert witness to the standards set out in Kennedy v Cordia, on the basis that ‘’his evidence as to the choice of valuation methodology was in essence and he himself accepted, merely his say-so’’ and ‘’moreover, he had no contemporary, real world valuation experience’’. This was rejected by Lord Clark on the basis that the expert ‘’obviously offered opinion evidence, but it was not, as suggested, ‘’merely his say-so’’... rather than being unsubstantiated ipse dixit, it was based upon quite standard features of the EBITDA approach.’’ The judge went on to say that the expert ‘’did have appropriate experience…’’ and that he explained ‘’with reasons why the EBITDA approach for valuation… was to be preferred.’’
Expert’s duty to disclose prior connections
Joint Liquidators of RFC 2012 plc, Noters  CSOH 99 concerned an application by the joint liquidators of a football company under the Insolvency Act 1986.
Lord Tyce addressed certain issues regarding the responder’s expert, Mr David Bulcher, stating that although he did not hold the expert’s evidence as inadmissible (on the basis of Kennedy v Cordia), it must be treated with caution owed to the fact that his connections with one of the owners of the football company were not disclosed in his expert report. The explanation given by senior counsel failed ‘to have proper regard to the duty incumbent upon Mr Bulcher himself to disclose prior connections.’
Expert witnesses are assumed to be aware of and understand the terms of their appointment, including their duty to the court and the extent and limits of their role. As an expert witness skills and disciplines are different to those of an expert’s day job, the above cases emphasise the value of regular and up to date professional training to an expert witness to ensure that they are kept abreast of all the key developments in common law regarding the scope of their duty and its application. Instructing solicitors are advised to bear this in mind when appointment and working with expert witnesses.